I know this is a violation via the User Agreement, but I have a different question.
Is one able to report a "Suspected Account Sharer? Would they be able to run IP checks or traces, or at least send a warning letter about “possible account sharing”, and consequences if they continue, so both parties are alert and aware about this?
There really is no mechanism for reporting this. We often hear about these cases when someone sells off saved mats, or uses the combined gold to make a purchase for a personal character. In other words, we hear about it when the sharing fails. And, as pointed out, there’s nothing we can do to solve the problem when it lies between two people willingly sharing an account.
So you could submit a ticket if you wish, but quite honestly it won’t be a priority to investigate. Fact is, we’ll probably hear about it at some point anyway, since these things so often blow up. 
